<p>(3) Have you googled? I found this page that appears to have registration information:
[American</a> Mathematics Contest 12 - AMC 12](<a href=“American Mathematics Competitions | Mathematical Association of America”>American Mathematics Competitions | Mathematical Association of America)</p>
<p>(4) If you’re interested in math and science, you could try RSI, MITERS (if you’re a minority), or WTP (if you’re female). You can google these from MIT’s website. There are more non-MIT-affiliated programs, but I am not familiar with them.</p>